The present invention relates to a molded capacitor.
A molded capacitor is made by connecting a plurality of capacitor elements electrically and molding the assembly with synthetic resin. With this type of capacitor in which the capacitor elements are covered by resin, impregnation of resin at the ends of the capacitor elements has to be sufficient. Otherwise, partial discharge will tend to occur, thus causing breakdown of the capacitor. But it is very difficult or almost impossible to completely impregnate the capacitor elements with synthetic resin at their recessed end portions. Thus, the capacitor elements tend to suffer from corona discharge at their end portions.
With the prior art molded capacitors, this problem is tackled by reducing the voltage assigned to each capacitor element. This increases the number of capacitor elements and makes the capacitor bulky and expensive.
In light of the above drawbacks with prior art molded capacitors, the present inventors have conceived the idea of encasing each capacitor element in a stiff container, filling an insulating gas therein, and molding the containers with synthetic resin.
With prior art molded capacitor, each capacitor element is vacuum-packed in a flexible synthetic resin film pack and an insulating gas is filled in the film pack. With this type capacitor, it is relatively easy to vacuum-pack the capacitor elements and then fill the film packs with an insulating gas. But the insulating gas in the film packs expands or contracts in molding the vacuum-packed capacitor elements with synthetic resin, so that air gaps are liable to develop between the film packs and the molding resin. The air gaps may induce corona discharge. If the film packs are in tight contact with the molding resin and no air gaps develop therebetween, the film packs cannot contract after they have expanded by the temperature rise during molding. This will cause the pressure of the insulating gas in the film packs to drop, thus lowering the corona discharge starting voltage.